Things to consider in sizing a UPS and load

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Issue:
Proper Unit and load sizing

Product Line:
All APC units

Environment:
All Models, All Serial Numbers

Cause:
We at Schneider Electric values the importance of providing the right unit for your needs, ensuring a reliable and efficient operation of your critical equipment.
If the UPS is undersized for the connected load, it may result in frequent overloading and overheating, leading to potential UPS failure and inadequate power backup during outages. On the other hand, oversizing the UPS for a small load can lead to inefficiency and higher operating costs.

Properly sizing the UPS and load is essential to ensure optimal performance, efficiency, and reliability of the electrical system. It's important to conduct thorough load assessments to determine the right capacity for both the UPS and the connected load.

Resolution:

It is important to always consider the following when sizing a unit:

Section 1 : Topology

Currently some Back UPS units uses the standby topology, and the Backs UPS Pro units uses line interactive. Smart UPS units still also uses the line interactive, and double conversion online.

Detailed information about the differences of the topologies is further discussed in FA15744 . Note that a double conversion online is recommended if the load has redundant power supplies and/or requires an Automatic Transfer Switch. Please refer to our online article FAQ000235550.

Section 2 : Input Requirements

When considering the input requirements of a UPS, several key factors should be taken into account:

Plug Type: Identify the specific plug type (e.g., NEMA, IEC) used in the installation area and ensure that the UPS has a matching input plug to seamlessly connect to the power source.
Voltage and Amperage Rating: Verify that the UPS input plug aligns with the voltage (120v, 208v or 240v) and amperage rating (15a, 20a or 30a) of the power outlet to prevent overloading or compatibility issues.
Locking Mechanism: In environments where vibration or movement is a concern, consider UPS units with locking input plugs to secure the connection and prevent accidental disconnection.
Frequency Tolerance: Verify that the UPS is designed to operate within the standard input frequency range of the local power supply. Common frequencies include 50 Hz and 60 Hz.
Input Waveform Compatibility: Determine if the UPS supports the required input waveform (sinewave, square wave, etc.) for the connected equipment.
Single-phase or Three-phase: Identify whether the load requires single-phase or three-phase input power to select the appropriate UPS configuration.
Input Protection Features: Consider any specific input protection features needed, such as surge protection or input line filtering.
Note: In Double Online Conversion, the power is always filtered since it passes through a rectifier then to the charger. The charger then feeds the battery where the battery then feeds an inverter which then converts DC battery power to AC Voltage used to feed the load. Meaning, there will be no means that a surge or any power irregularity will pass to the load "while the unit is at an online state". More details on Double Online Conversion also is discussed in page 7 of APC by Schneider Electric White Paper # 1.

Section 3 : Transfer time

For home and personal use, you may consider getting our Back UPS and Back UPS Pro, More details on our online article FA158892.

For small business and Data Centers, due to the certain needs of your equipment, it is recommended to consider getting units under the Smart UPS units. Line interactive units have transfer time while Double Conversion Online has no transfer time, further details are discussed in FAQ000268416 .

Section 4 : Placement

In locations with consistent dirty power, it's critical to prioritize buying a new UPS with voltage regulation, surge protection, and noise filtering capabilities to safeguard sensitive equipment from power fluctuations and electrical noise.

When it comes to MDF (Main Distribution Frame) sites, where critical network infrastructure is housed, selecting a UPS with high reliability and remote management capabilities is essential. Additionally, considering factors such as redundancy, maintenance bypass options, and seamless integration with existing infrastructure becomes crucial for uninterrupted operations.

In both scenarios, assessing the specific power quality challenges and the unique requirements of the equipment being protected is key to selecting the most suitable UPS solution.

Section 5 : Sizing and Runtime

Sizing a UPS to its maximum capacity is not ideal. It's important to consider a margin of safety and to avoid operating the UPS at full capacity for extended periods. Sizing the UPS with some headroom ensures that it can handle peak loads and allows for future expansion of the connected load without requiring an immediate UPS upgrade.

Additionally, operating a UPS near its maximum capacity can lead to decreased efficiency, higher heat generation, and a reduced battery runtime, potentially impacting the overall reliability of the system.
Therefore, it's generally recommended to size the UPS with the connected load that is comfortably within the UPS capacity, preferably around 80% of the UPS' maximum capacity to allow for flexibility and optimal performance.

Sample:
SMT1500C: 1000W x 80% = 800W
Runtime estimate: 9mins 34s
If on full load of 1000W, runtime estimate: 6mins 30s

As you will notice below, the runtime estimate is much lower as the UPS reach its maximum capacity.
SMT1500C Estimated Runtime

Below shows the graph and runtime estimate of the SMT1500C, as it reach its maximum capacity.

SMT1500C runtime graph

*Note: This is for sample purposes only, runtime may vary depending on unit and load. Always check the runtime graph of each unit.

If you have any clarifications and/or requests for the above mentioned available information, please feel free to contact us at 1-800-800-4272 or chat with our technical support representatives.